Some coating applications require relatively thick films. For example, coatings to be applied to substrates such as, for example, modified bitumen single-ply roofing membranes used on industrial building roofs, are conventionally on the order of 10-40 mils (0.02-0.10 cm.) thick. Such coatings are frequently referred to as "roof mastics" although "mastic coatings" as used herein includes any such thick coating applied to a substantially horizontal surface such as, for example, a roof deck, to a substantially vertical surface such as, for example, a wall, or to other substrate surfaces. In some cases, the substrate surfaces to which it is desired to apply mastic coating(s) present problems such as, for example, difficulty in adhesion of the mastic coating to the substrate or such as, for example, the presence of highly colored bodies in or on the substrate which may migrate into and discolor the mastic coating. The tiecoats of this invention, disposed between the substrate and the mastic coating, solve such problems without unduly complicating or hindering the objective, the application of an effective mastic coating system.